Discrimination of maleic hydrazide polymorphs using terahertz spectroscopy and density functional theory

Abstract:

The terahertz (THz) absorptions of maleic hydrazide polymorphs (MH2 and MH3) have been measured utilizing terahertz time-domain spectroscopy (THz-TDS). MH2 and MH3 have displayed totally different THz absorption features compared to their basically identical infrared spectral peaks. Experimental THz spectrum of MH2 showed six distinct absorption features while MH3 demonstrated five characteristic absorption peaks in the range of 10—160 cm-1. Spectral interpretation has been carried out in the framework of density functional theory (DFT) using periodic unit cell models. The simulation yields a good quality with respect to the measured features. Further analysis into the mode of vibration showed that the low-frequency THz spectral features (<112 cm-1) are contributed by intermolecular interactions mediated by in-plane/out-of-plane collective vibrations. The varied intermolecular interactions and crystal habits are the primarily reason for the THz spectral differences of MH2 and MH3.